The present invention relates to aircraft engine systems and, more particularly, to a compressor discharge temperature (T3) sensing system as the baseline production design for a turbo-fan engine.
Existing systems used to measure T3, i.e., compressor discharge, air flow are primarily thermocouple sensors mounted in the compressor flow stream. These sensors require access into the flow path through the compressor case. Unfortunately, this exposes the engine turbo-machinery to potential mechanical failures of the sensor which could cause it to fall into the flow path. Additionally, the relatively slow air velocity into the compressor discharge area causes the sensor to have a relatively long time constant. This long time constant leads to significant inaccuracies, on the order of 10-15%, in measuring the air temperature during critical transient maneuvers of the aircraft engine. The maximum acceptable inaccuracy is approximately 2-3% during engine transients.
Compressor discharge temperature is critical in certain situations, such as in staging a dual annular combustor for a high bypass turbofan commercial jet engine. Specifically, the T3 measurement is used in calculating air flow into the combustor. The staging strategy is based in part on the combustor fuel-to-air flow ratio. The staging of the combustor is critical to meet the engine operability needs, i.e., flameout margin, and emissions goals.
It is therefore highly desirable and an object of the present invention to provide a T3 sensing system which provides improved compensation and may be mounted external to the flow path.
Another object of the present invention is to provide such a T3 sensing system wherein access into the direct flow path is not required.
Another object of the present invention is to provide a more accurate transient T3 signal.
These objects and other features and advantages will become more readily apparent in the following description when taken in conjunction with the appended drawings.